Bacterial motility patterns adapt in response to spatial confinement and disorder*

Motility is essential for bacteria thriving in a wide range of crowded and unstructured natural habitats such as biological tissues, soil, and sediments. Recent work employing novel porous hydrogel landscapes demonstrated that Escherichia coli motility patterns deviate from the well-characterized ‘run-and-tumble’ behavior in highly confined, spatially structured environments. Here, we introduce a simple microfluidics device to examine how interactions with spatially complex mechanical cues shape bacterial motility. We precisely tune several environmental parameters in the 2D micro-environment (e.g., the level of confinement and disorder) by varying the density of pillar-like structures and their positional noises. Our experiments focus on two motility types represented by wild-type strains of E. coli (‘run-and-tumble’ swimmer) and P. aeruginosa (‘run-reverse’ swimmer). We track individual cells as they move through pillar landscapes and quantify key motility metrics, including mean square displacement, velocity, and run length. Our work advances our understanding of bacterial locomotion within varying environmental regimes and further emphasizes the significance of factoring in environmental structures when conducting bacterial motility studies.